The present invention relates to a method for diagnosing deterioration of an article (typically a cable) having at least a covering layer made from an organic polymer material and an apparatus therefor.
A covering layer (insulating layer made from an organic polymer material) of an installed cable changes with the time elapsed due to various factors and shows degraded electric insulating property. To prevent this, a periodic inspection is necessary to diagnose deterioration level. For this purpose, various deterioration diagnostic methods have been proposed.
Of the proposed methods, the method for diagnosis of deterioration by propagating an ultrasonic wave (JP-A-7-35732, JP-A-7-35733) is superior in that it does not require destruction of the cable. The method described in these publications includes propagating an ultrasonic wave through the covering layer of the installed cable, based on which an ultrasonic wave propagation velocity is calculated, and converting the velocity to physical property such as breaking elongation percentage and hardness of the covering layer. The level of deterioration is diagnosed based on the obtained property.
The measurement method of the propagation velocity in the above-mentioned publications using an ultrasonic wave is outlined in the following. An ultrasonic wave enters from the surface of the covering layer of the cable toward the center of the cable, and the time t is measured, which is necessary for the ultrasonic wave to reflect from the interface between the covering layer and the layer beneath (e.g., conductor) and to return to the position of incidence. Using this t and the thickness a of the covering layer, V=2a/t is calculated. This V is taken as the propagation velocity of ultrasonic wave in the covering layer.
The measurement method of the above-mentioned publications is problematic in that it uses thickness a of the covering layer for the calculation of propagation velocity V of the ultrasonic wave. Namely, when the thickness a of the covering layer can be known with high precision, the above-mentioned measurement method is useful, but the value a cannot be known accurately with regard to an actually installed article, such as a cable, which does not permit breakage. By referring to a design specification, for example, the standard size a as designed can be known, but the actual size of a may be considerably different because a production tolerance of xc2x115% of the standard size on design is allowed for the production of an insulating electric wire. Therefore, the propagation velocity calculated using the value a obtained in a non-destructive manner and the deterioration diagnosis based thereon show low precision.
It is therefore an object of the present invention to provide a more preferable deterioration diagnostic method for diagnosing deterioration level of an article (e.g., cable) having at least a covering layer made from an organic polymer material, by the use of an ultrasonic wave, as well as a deterioration diagnostic apparatus preferable for practicing the method.
The deterioration diagnostic method of the present invention is a method for diagnosing deterioration of an article having at least a covering layer made from an organic polymer material. The method is characterized in that the deterioration diagnostic characteristic and the corresponding ultrasonic wave propagation characteristic of a covering layer sample are measured, a data group for the deterioration diagnosis is formed, wherein the value of deterioration diagnostic characteristic and the value of ultrasonic wave propagation characteristic correspond to each other, an ultrasonic wave is propagated through the surface and near surface of the covering layer of an article to measure the ultrasonic wave propagation characteristic of the covering layer, and the deterioration diagnostic characteristic corresponding to the ultrasonic wave propagation characteristic is obtained from the aforementioned data group.
The deterioration diagnostic method of the present invention comprises the steps of changing, when preparing the data group for the deterioration diagnosis, the material specification consisting of one or more factors selected from the group consisting of the kind of the organic polymer material, the kind of plasticizer contained in this organic polymer material, the amount of plasticizer added, the amount of filler added, and the amount of carbon added, and measuring deterioration diagnostic characteristic and ultrasonic wave propagation characteristic corresponding thereto of samples having different material specifications to form a data group for deterioration diagnosis, measuring the ultrasonic wave propagation characteristic of the covering layer of an article, and obtaining the deterioration diagnostic characteristic corresponding to the aforementioned ultrasonic wave propagation characteristic from the data group having the material specification equivalent to this covering layer.
In the deterioration diagnostic method of the present invention, the above-mentioned ultrasonic wave propagation characteristic is the propagation velocity of an ultrasonic wave, which is measured by setting an ultrasonic wave transmitting means and an ultrasonic wave receiving means on the surface of a measurement target respectively via a delay chip, thereby to make an ultrasonic wave sent from the aforementioned transmitting means linearly propagated in the measurement target to the position of the aforementioned receiving means and received by the receiving means, measuring propagation times t1 and t2 of the ultrasonic wave when the intervals between the aforementioned transmitting means and the aforementioned receiving means are L1 and L2, respectively, and calculating (L2xe2x88x92L1)/(t2xe2x88x92t1) to give the propagation velocity of the ultrasonic wave.
In the deterioration diagnostic method of the present invention, the above-mentioned ultrasonic wave propagation characteristic is the propagation time of an ultrasonic wave that has been transmitted a certain distance. The covering layer of a specimen or article is the test target, and an ultrasonic wave transmitting means and an ultrasonic wave receiving means are each set on the surface of the test target via a delay chip at the aforementioned certain distance. Then, the time necessary for the ultrasonic wave sent from the aforementioned transmitting means to be linearly transmitted through the test target to the position of the aforementioned receiving means and to be received by the receiving means via the delay chip is measured.
The deterioration diagnostic method of the present invention measures the distribution of the deteriorating factors that cause deterioration of the covering layer of the above-mentioned article, which is an installed cable, in the longitudinal direction of the cable and make a diagnosis of the portion showing greater levels of deteriorating factors.
According to the deterioration diagnostic method of the present invention, the above-mentioned deterioration diagnostic characteristic value of the covering layer of an article is taken as E1; a heating temperature t and the corresponding heating time h at various deterioration diagnostic characteristic values are measured after changing the deterioration diagnostic characteristic values, inclusive of limit of use value Ez, for a specimen made of the same material as the covering layer, thereby to give a data group used for remaining life prediction; using this data group for remaining life prediction, wherein the period of use of the aforementioned article is regarded as a heating time h1, the heating temperature t1 corresponding to the heating time h1 at the deterioration diagnostic characteristic value of E1 is determined; the heating time hz corresponding to the heating temperature t1 at the limit of use value Ez of the deterioration diagnostic characteristic is determined; and the value of hzxe2x88x92h1 is taken as the remaining life.
The deterioration diagnostic apparatus of the present invention is an apparatus for diagnosing the deterioration of an article having at least a covering layer made from an organic polymer material and comprises at least the measuring device of the following (A):
(A) a measuring device for ultrasonic wave propagation characteristic wherein a covering layer of an article or a specimen of a covering layer is a measurement target, comprising an ultrasonic wave transmitting means, an ultrasonic wave receiving means, a delay chip of the following (A1) to be intervened when these means are set on the surface of the measurement target, and a propagation time measuring means to measure the time spent from transmission of an ultrasonic wave from the aforementioned transmitting means to its receipt by the receiving means:
(A1) a delay chip whose inclination and material have been determined such that the propagating direction of the ultrasonic wave changes when it enters the measurement target from the delay chip, as a result of which the ultrasonic wave is propagated through the surface and near surface of the measurement target.